1. Field of the Invention
An aspect of this disclosure relates to a protection circuit for a secondary battery, a battery protection module, a battery pack, and a method.
2. Description of the Related Art
Electronic apparatuses driven by a battery pack including a secondary battery have become popular, and various proposals have been made for configurations of battery packs (see, for example, Japanese Patent No. 5110168).
FIG. 6A through 6C are schematic diagrams illustrating a configuration of an exemplary related-art battery pack 640. As illustrated by FIG. 6A, the battery pack 640 includes a secondary battery 641, input-output terminals 642 and 643 that are connected to an electronic apparatus 650 and/or a battery charger, a thermistor 644 for detecting a temperature of the secondary battery 641, and a battery protection module 630. The battery protection module 630 includes a semiconductor integrated circuit (IC) 610 used as a protection circuit for the secondary battery 641. The semiconductor integrated circuit 610 connects the cathode of the secondary battery 641 with the positive input-output terminal 642, and connects the anode of the secondary battery 641 with the negative input-output terminal 643.
Also, each of a first field-effect transistor (FET) 631 that is a switch for turning battery charging on and off and a second FET 632 that is a switch for turning battery discharging on and off is connected in series to the semiconductor integrated circuit 610.
The configuration of the battery pack 640 of FIG. 6A, for example, makes it possible to prevent charging of the secondary battery 641 by turning off the first FET 631 when the temperature of the secondary battery 641 becomes greater than or equal to a predetermined threshold, and thereby makes it possible to prevent the secondary battery 641 from heating up.
Here, assume a case where the electronic apparatus 650 driven by the battery pack 640 is a power tool, and the battery pack 640 is connected to drive the power tool while the temperature of the secondary battery 641 is greater than or equal to the predetermined threshold and charging of the secondary battery 641 is prevented. In this case, because the temperature of the secondary battery 641 is greater than or equal to the predetermined threshold, the secondary battery 641 discharges electricity with the first FET 631 turned off.
When the first FET 631 is off, electricity is discharged via a parasitic diode 631d of the first FET 631 (see a dotted arrow line in FIG. 6B). As a result, the power consumption of the first FET 631 increases and the first FET 631, which is a switch, heats up.
To discharge electricity without using the parasitic diode 631d of the first FET 631 when the first FET 631 is off, separate paths may be provided for charging and discharging as illustrated by FIG. 6C. However, this approach makes it necessary to change the system (or configuration) of the electronic apparatus 650 and therefore increases costs.
For the above reasons, there is a demand for a battery pack with a configuration that can prevent heat-up resulting from discharging even when the battery pack is connected to an electronic apparatus while charging of the secondary battery is prevented due to heat-up of the secondary battery, and that does not require changing the system (or configuration) of the electronic apparatus.